Re: [lmi] Safe and consistent dereferencing and casting [Was: Code review: product editor]

[Evgeniy Tarassov]

On 4/13/07, Vadim Zeitlin <address@hidden> wrote:
>  Basically there are 2 options for implementing this function:
[...]
> I strongly prefer the second form as I don't like provoking an exception
> which we then immediately proceed to catch and ignore but Evgeniy thinks
> that the first version is more clear (while for me it's exactly the
> contrary). What do you think about this?

Oh, let me just slightly complete the code, since there are two
different checks:
- one for the pointer to be non-NULL
- another one for the pointer to be of the correct type

   template <typename T, typename U>
   T& safely_dereference_as(U *ptr)
   {
       if(!ptr)
           {
           fatal_error() << "Pointer could not be NULL" << LMI_FLUSH;
           }
       try
           {
           return dynamic_cast<T>(*ptr);
           }
       catch(std::bad_cast const& e)
           {
           fatal_error() << "Object is of a wrong type: " << e.what()
<< LMI_FLUSH;
           }
   }

or

   template <typename T, typename U>
   T& safely_dereference_as(U *ptr)
   {
       if(!ptr)
           {
           fatal_error() << "Pointer could not be NULL" << LMI_FLUSH;
           }
       T *p = dynamic_cast<T *>(ptr);
       if ( !p )
           {
           fatal_error() << "Object is of a wrong type: " << e.what()
<< LMI_FLUSH;
           }
       return *p;
   }

Anyway the question remains the same.

--
Best wishes,
Evgeniy Tarassov